This is an in circuit transistor
(and
FET and diode) tester that uses a 1 kHz AC square wave test
signal. The patented test method made this a popular
In-Circuit
transistor test meter and it was made in versions A, B, C and D.
This unit is also labeled as an III model 350 In Circuit
Transistor Tester.
Although the DC battery check worked
OK
when this used instrument arrived when trying to measure the beta
of a
transistor, they all test as infinite beta (equivalent to no
deflection
of the meter (all the way to the left)). The Beta Cal
function
works as it should and the instrument passes the tests in the
-14-3
manual. This may mean the beta is in the hundreds but when
the
transistor is removed from the socket it also reads infinite
beta. I see this as a flaw in the design. The tester
may
work used for In-circuit testing, but does not work for loose
transistors.
When DC stuff works and
AC stuff does not then old electrolytic capacitors are
suspect.
In this case there are a number of high impedance caps that need
to be
replaced.
After
removing
the 4 cover screws and the 4 screws on the rear PCB, the rear
PCB can be hinged open allowing replacement of the caps. The
photo at the left shows the stock meter, except I've put a black
dot by
the negative lead of all the electrolytic caps. It turns out
that
on the trace side of the PCB there are small "+" marks for each of
the
electrolytic caps. After replacing C5, C6, C7, C10, C11, C14
and
C15 (all with 22 uF 25 V) the meter is still not working
correctly. The beta zero works but not the beta test on a
loose
transistor.
If you have an idea of what's going on, please
let me know.
During the troubleshooting process I made a copy of the overall
schematic and set the switches for Beta X10 and NPN then erased
all non
connected paths. The resulting diagram is considerably
different
from Fig 5-2 in the 14-3 TM. In particular Fig 5-2
shows
emitter DC bias being a 3k9 resistor to +6 volts, but there is not
DC
connection between the transistor the battery ground. There
is a
DC voltage of 2.8 Volts between all three transistor terminals and
battery ground, but not bias. This measurement is consistent
with
the overall schematic diagram.
2894206
Transistor Beta Tester, George Franklin Montgomery (Dept of
Commerce),
Jul 7, 1959,
324/765 - blocking oscillator
2907954
Transistor test set,
Jr
Arthur J Radeliffe,
ITT,
1959-10-06, -
2922954
Circuit Tester, John F. Bigelow (Philco), Jan 26, 1960,
324/765
- In circuit transistor tester
3051900
In-circuit transistor tester,
Zechter
Sol,
Gruen
Harold,
Space
Systems Loral (Philco), 1962-08-28, -
3227953
Bridge Apparatus for Determining the Input Resistance and Beta
Figure for an In-circuit Transistor, W.J. Cerveny (Hickok), Jan 4
1966,
calls:
2578455 - testing AC resistance in live circuit
2866948 Test Circuit for Interconnected Components, R.P. Witt
(Army),
Dec 30 1958 -
2925554 Resistance Checker, M.H. Hayes (Link Aviation), Feb 16
1960, -
for analog computer parts
2932789
3370233
Test Apparatus for Determining Beta and Leakage Current of an
In-circuit or Out-of-circuit Transistor, Oliver James Morelock
(Triplett), Feb 1968,
324/768 ; 2/160; 324/119 - includes
glove
where three fingers position three probes
4801878
In-circuit transistor beta test and method, R.J. Peiffer, D.T.
Crook (HP), Jan 31, 1989,
324/765 -
TS-1836
3287643
Method and Apparatus for
Measuring the
Beta Parameter of an In-Circuit
Transistor without the Application of D.C. Biasing Thereto
Nov.
22,
1966 B. Reich (AEL)
324/768
- In-Circuit test in a way that won't damage the
transistor and that will work in spite of the surrounding
circuit. The transistor is operated as a common base
amplifier
with the emitter driven by an ac coupled square wave. This
causes
the collector to self bias by rectifying the emitter signal and
thus
produce a DC current.
3440530
Method and Aparatus for Measuring
the
Resistance of an Electrical
Component which may be Shunted by a Semiconductor Device
April
22,
1969, B. Reich
324/713
- the idea is that small signals do not
turn on semiconductors.
3458814
Tester for Determining the
Material
Type of Transistors, Ryan (AEL), Jul 29 1969,
324/766
-
reading now
[an error occurred while processing this directive] page created 16 April
2006.
After
removing
the 4 cover screws and the 4 screws on the rear PCB, the rear
PCB can be hinged open allowing replacement of the caps. The
photo at the left shows the stock meter, except I've put a black
dot by
the negative lead of all the electrolytic caps. It turns out
that
on the trace side of the PCB there are small "+" marks for each of
the
electrolytic caps. After replacing C5, C6, C7, C10, C11, C14
and
C15 (all with 22 uF 25 V) the meter is still not working
correctly. The beta zero works but not the beta test on a
loose
transistor.